Analysis of Specific Th1/Th2 Helper Cell Responses and IgG Subtype Antibodies in Anti-CD4 Monoclonal Antibody Treated Mice with Autoimmune Cardiomyopathy

The cytokine repertoire of ADP/ATP carrier-specific humoral immune responses and the cytokine-dependent anti-ADP/ATP carrier antibody IgG subclasses were examined in a cohort of ADP/ATP carrier-immunized BALB/c mice treated with anti-CD4 monoclonal antibody. Eighteen male BALB/c mice （6–8 weeks old） were randomized into 3 groups： dilated cardiomyopathy （DCM） group, DCM-tolerance （Tol） group and control group. The mice in DCM group were immunized with the peptides derived from human ADP/ATP carrier protein for 6 months and mice in the control group were sham-immunized, while the mice in DCM-Tol group were immunized with ADP/ATP carrier protein and anti-CD4 McAb simultaneously. Serum autoantibody against ADP/ATP carrier and IgG subclasses were measured by ELISA, intracellular cytokines IFN-γ and IL-4 of Th cells were moni- tored with flow cytometry, and splenic T cell cytokines IFN-γ, IL-2, IL-4 and IL-6 were detected by using real-time fluorescent quantitative PCR. The results showed that the autoantibody against ADP/ATP carrier was found in all mice in DCM group, and the antibody level, serum IgG1 and IgG2a subclasses, cytokines in T cells and Th cells were all elevated in DCM group, as compared with those in control group （P〈0.01）. On the other hand, in DCM-Tol group, the autoantibody level and contents of all the cytokines were significantly different from those in DCM group （P〈0.01）, and were close to those in control group. And the levels of IgG1, IgG2a, IgG2b and IgG3 were influenced, to varying degrees, by anti-CD4 McAb as compared with those in DCM group. All these four types of IgG subclasses were substantially decreased in DCM-Tol group as compared with DCM group. It is concluded that the treatment with anti-CD4 McAb could prevent the activation of T cells, reverse the abnormal secretion of cytokines and the imbalance between Th1/Th2 cell subsets and abnormal production of autoantibody against ADP/ATP carrier, and eventually avoid myocardial injuries.     

Effect of oxidative stress on ventricular arrhythmia in rabbits with adriamycin-induced cardiomyopathy

The purpose of the present study was to examine the effects of oxidative stress on ventricular arrhythmias in rabbits with adriamycin-induced cardiomyopathy and the relationship between oxidative stress and ventricular arrhythmia. Forty Japanese white rabbits were randomly divided into four groups (n=10 in each): control group, metoprolol (a selective β1 receptor blocker) group, carvedilol (a nonselective β blocker/α-1 blocker) group and adriamycin group. Models of adriamycin-induced car-diomyopathy were established by intravenously injecting adriamycin hydrochloride (1 mg/kg) to rabbits via the auri-edge vein twice a week for 8 weeks in the adriamycin, metoprolol and carvedilol groups. Rabbits in the control group were given equal volume of saline through the auri-edge vein. Rabbits in the metoprolol and carvedilol groups were then intragastrically administrated metoprolol (5 mg/kg/d) and carvedilol (5 mg/kg/d) respectively for 2 months, while those in the adriamycin and control groups were treated with equal volume of saline in the same manner as in the metroprolol and carvedilol groups. Left ventricular end diastolic diameter (LVEDd) and left ventricular ejection fraction (LVEF) were measured by echocardiography. Plasma levels of N-terminal pro B-type natriuretic peptide (NT-proBNP), malondialdehyde (MAD) and superoxide dismutase (SOD) were detected. The left ventricular wedge preparations were perfused with Tyrode’s solution. The transmural electrocardiogram, transmural action potentials from epicardium (Epi) and endocardium (Endo), transmural repolarization dispersion (TDR) were recorded, and the incidences of triggered activity and ventricular arrhythmias were obtained at rapid cycle lengths. The results showed that TDR and the serum MDA and NT-proBNP levels were increased, and LVEF and the serum SOD level decreased in the adriamycin group compared with the control group. The incidences of triggered activity and ventricular arrhythmia were significantly higher in the adriamycin group than those in the control group (P<0.05). In the carvedilol group as compared with the adriamycin group, the serum SOD level and the LVEF were substantially increased; the TDR, and the serum MDA and NT-proBNP levels were significantly decreased; the incidences of triggered activity and ventricular arrhythmia were obviously reduced (P<0.05). There were no significant differences in the levels of MDA and SOD, LVEF, TDR and the incidences of triggered activity and ventricular arrhythmia between the adriamycin group and the metoprolol group. It was concluded that carvedilol may inhibit triggered activity and ventricular arrhythmias in rabbit with adriamycin-induced cardiomyopathy, which is related to the decrease in oxygen free radials.     

Role of natural killer T cells in Graves’ disease

Objective To explore the role of natural killer T (NK T) cells in the pathogenesis of Graves’ disease.Methods NK T cell deficient mice and wild BALB/c mice were immunized with cells expressing TSH receptor once every two weeks 6 times. Two weeks after the final immunization, the mice were killed and serum thyroxine levels, anti-TSH receptor antibodies and thyroid pathological changes were examined.Results The mean levels of TT 4 and TRAb in the immunized NK T cell deficient group were slightly elevated but significantly different from those of the non-immunized control group, while comparable to those in the immunized wild group. There were no significant changes of the activity levels of TSAb or TSBAb in the immunized NK T cell deficient mice compared to those in immunized wild control mice. Thyroids from immunized NK T cell deficient mice showed mild hypertrophy of some follicles as compared with non-immunized control mice. This change was comparable to immunized wild control mice.Conclusion NK T cells may not be involved in the pathogenesis of Graves’ disease.     

A therapeutic anti-CD4 monoclonal antibody inhibits T cell receptor signal transduction in mouse autoimmune cardiomyopathy

Background T cell immune abnormalities in patients with dilated cardiomyopathy (DCM) has been intensively studied over the past 10 years. Our previous study has suggested that immunization of mice with the peptides derived from human adenine nucleotide translocator (ANT) result in the production of autoantibodies against the ANT and histopathological changes similar to those in human DCM. The ANT peptides can induce autoimmune cardiomyopathy like DCM in Balb/c mice. In this study we aimed to focus on the molecular mechanism of T cells in the autoimmune cardiomyopathy mouse model by detecting the expression of the two T cell signaling molecules.Methods The ANT peptides were used to cause autoimmune cardiomyopathy in Balb/c mice. Anti-L3T4 or rat anti-mouse IgG was administered to the mice (n=6 in each group) simultaneously immunized with ANT. ELISA analysis was used to detect autoantibodies against the ANT peptides and the percentages of interferon-γ and interleukin-4 producing cells among splenic CD4(+) lymphocytes was determined by using flow cytometry analysis. The expression of CD45 in spleen T cells was determined by immunohistochemistry and the mRNAs of T cell signaling molecules were detected by real-time PCR.Results Treatment of ANT immunized Balb/c mice with anti-CD4 mAb caused a reduction in the gene expression of P56lck and Zap-70 and a lower level of CD45 expression by spleen T cells. Also, a reverse of the Th1/Th2 ratio that results in the reduced production of antibodies against ANT was found in the anti-CD4 monoclonal antibodies (mAb) group. Whereas irrelevant antibody (rat anti-mouse IgG) did not suppress T cell signaling molecules nor inhibit CD45 expression, and control-antibody mice did not show any significant differences compared with the DCM group.Conclusion The results show that anti-CD4 mAb is a powerful inhibitor of the early initiating events of T cell receptor (TCR) signal transduction in mouse autoimmune dilated cardiomyopathy.     

Expression of NADPH oxidase and production of reactive oxygen species in aorta in an active immunization mouse model with AT1-EC2 peptide

The antibody against AT1-EC2 plays a role in some kinds of inflammatory vascular diseases including malignant hypertension,preeclampsia,and renal-allograft rejection,but the detailed mechanisms remain unclear.In order to investigate the changes of NADPH oxidase and reactive oxygen species in the aorta in a mouse model which can produce AT1-EC2 antibody by active immunization with AT1-EC2 peptide,15 mice were divided into three groups:control group,AT1-EC2-immunized group,and AT1-EC2-immunized and valsartan-treated group.In AT1-EC2-immunized group and AT1-EC2-immunized and valsartan-treated group,the mice were immunized by 50 μg peptide subcutaneously at multiple points for 4 times:0,5,10,and 15 days after the experiment.In AT1-EC2-immunized and valsartan-treated group,valsartan was given at a dose of 100 mg/kg every day for 20 days.After the experiment,the mice were sacrificed under anesthesia and the aortas were obtained and frozen in liquid nitrogen for the preparation of frozen section slides and other experiments.The titer of AT1-EC2 was assayed by using ELISA.The level of NOX1 mRNA in the aorta was determined by using RT-PCR.The expression of NOX1 was detected by using Western blotting.Confocal scanning microscopy was used to assay the α-actin and NOX1 expression in the aortic tissue.The O 2.production was detected in situ after DHE staining.The mice produced high level antibody against AT1-EC2 in AT1-EC2-immunized group and AT1-EC2-immunized and valsartan-treated group,and the level of NOX1 mRNA in the aortic tissues was 1.6±0.4 times higher and the NOX1 protein expression was higher in AT1-EC2-immunized group than in control group.There were no significant differences in the level of NOX1 mRNA and protein expression between control group and AT1-EC2-immunized and valsartan-treated group.The expression and co-localization of α-actin and NOX1 in AT1-EC2-immunized group increased significantly as compared with those in control group,and the O 2.production increased about 2.7 times as compared with contro     

Clinical significance and pathogenic role of anti-cardiac myosin autoantibody in dilated cardiomyopathy

Objective In order to explore the possible roles played by the autoimmune mechanism in the progression of myocarditis into dilated cardiomyopathy (DCM) using an animal model, we investigated whether autoimmune myocarditis might develop into DCM.Methods Experimental Balb/C mice (n = 20) were immunized with cardiac myosin with Freund‘s complete adjuvant at days 0, 7 and 30. The control Balb/C mice ( n = 10 ) were immunized with Freund‘s complete adjuvant in the same mannere. Serum and myocardium samples were collected after the first immunization at clays 15, 21 and 120. The anti-myosin antibody was examined by enzyme-linked immunosorbent assay and immunoblotting.Results Pathological findings demonstrated that there was myocardial necrosis or inflammatory infiltration during acute stages and fibrosis mainly in the late phase of experimental group, but the myocardial lesions were not found in the control group. Autoimmunity could induce myocarditis andDCM in the absence of viral infection. High titer anti-myosin IgG antibodies were found in theexperimental group, but not in the control group. Furthermore, the anti-myosin heavy chain (200 KD)antibody was positive in 21 of 48 patients with DCM and viral myocarditis, but only 4 of 20 patients with coronary heart disease, including 1 case and 3 cases that reacted with heavy and light chains(27. 5 KD), respectively. The antibodies were not detected in healthy donors.Conclusion Cardiac myosin might be an autoantigen that provokes autoimmunity and leads to the transformation of myocarditis into DCM. Detection of anti-myosin heavy chain antibody might contribute to diagnosis for DCM and viral myocarditis.     

Cardiac cytotoxic mechanism mediated by antibodies against myocardial mitochondrial ADP/ATP carrier in patients with dilated cardiomyopathy.

OBJECTIVE To investigate mechanism of the antibody-mediated cardiac cytotoxicity and clinical significance in dilated cardiomyopathy (DCM), and study the effects of the antibodies against the myocardial mitochondrial ADP / ATP carrier from sera of patients with dilated cardiomyopathy on the guinea pig ventricular myocytes.

METHODS This study included 18 patients with DCM (12 men and 6 women), with mean age of 43 years. Control group included 18 health donors, (9 men and 9 women), with mean age of 32 years. The antibodies against the ADP / ATP carrier and cell membrane 52 000 peptide were examined by immunoblotting. The antibody-mediated cardiac cytotoxicity was studied with the cytotoxic test and whole cell patch-clamp technique.

RESULTS The antibodies against myocardial mitochondrial ADP / ATP carrier and cell membrane 52 000 peptide were positive in 18 patients with DCM, while negative in controls. The antibodies induced cytotoxic damage with time-dependent and enhanced Ca-current in cardiac myocytes. The increasing amplitude of peak Ca(2+)-current was 100 pA-840 pA (n = 8) in different dilution of the antibodies. The effect of the antibodies might be inhibited by verapamil, and were null in controls (n = 4).

CONCLUSIONS The above findings suggest that an increase in the antibody-mediated Ca(2+)-current of cardiac myocytes is related to the cytotoxic damage in dilated cardiomyopathy.

     

EFFECTS OF β-ENDORPHIN ON PHYTOHEMAGGLUTININ -INDUCED LYMPHOCYTE PROLIFERATION AND MOUSE PLAQUE-FORMINGCELL RESPONSE VIA AN OPIOID RECEPTOR MECHANISM

The effects of opioid peptides on immune responses were investigated.It was found that β-endorphin(β-END) can depress proliferative responses to PHA in rat splenocytes but enhance those in mice,and it could also inibit the plaque-forming cell(PFC) response to sheep red blood cells when mouse splenocytes immunized in vivo were cultured in vitro with the peptide.The peptide antagonist naloxone was able to reverse β-END suppression of the PFC response.The data indicate that β-END suppresses antibody production or secretion via a specific opioidreceptor-mediated mechanism.     

SSB peptide and DNA co-immunization induces inhibition of anti-dsDNA antibody production in rabbits

Background Patients with systemic lupus erythematosus often have various autoantibodies. The relationship between these antibodies is still poorly understood. The aim of the present study was to observe the anti-SSB antibody and anti-dsDNA antibody production profiles following immunization with synthetic SSB peptide alone, DNA alone or co-immunization with these two antigens.
Methods SSB 214-225 aa peptide was synthesized by organic chemistry solid-phase peptide synthesis. Rabbits were immunized with the following antigens： synthetic SSB peptide linked with keyhole limpet hemocyanin （KLH）, DNA, SSB plus dsDNA, KLH and PBS. Antibodies were measured by ELISA. Histopathology and direct immufluorescence assays were also applied.
Results Anti-SSB and anti-dsDNA antibodies were produced following immunization with SSB peptide and DNA respectively. The level of SSB antibody in the co-immunization group was higher than that of the SSB peptide immunization group. The level of anti-dsDNA antibody in the co-immunization group was, however, lower than that in the DNA immunization group. Meanwhile, the level of anti-SSB antibody was higher than that of anti-DNA antibody in the co-immunization group. No morphological or immunological abnormalities were found in the heart, liver, kidney, spleen or skin tissues.
Conclusion Inhibition of anti-dsDNA-antibody was induced by co-immunization with synthesized SSB peptide and DNA, which might explain, at least partly, the mild disease in some LE subsets associated with SSB antibody.     

Effects of Bushen Huoxue Decoction on Nitric Oxide （NO） in Serum, Articular Cartilage and Synovium in Rabbits of Knee Osteoarthritis

Forty-eight New Zealand rabbits were divided into normal group(n=18),control group(n=18)andChinese herbs treatment group(n=12)randomly.The rabbits in the normal group receivedsham-operation,and the OA model was established by Hulth's method.All the rabbits in the treatmentgroup were given Bushen Huoxue Decoction(补肾活血汤)from the 6th week after the operation.At 6th,8th and 12th week after the operation,the NO concentrations of the serum,joint cartilage and synoviumwere examined.Results:Indicated that the NO concentrations of the serum,joint cartilage and synoviumin the control group were all significantly higher than those in the normal group,with the joint cartilagemore obvious(P<0.05).In the Chinese herbs treatment group the NO concentrations in all the partsobviously decreased as compared with the control group(P<0.05).It is suggested that Bushen HuoxueDecoction decrease the levels of NO in the serum,synovium and joint cartilage in the OA rabbit.     

用合成受体肽段长期免疫大鼠对其心脏结构和功能的影响

用合成的β1-受体功能表位肽段以及M2受体功能表位肽段肽连续18个月免疫大鼠,结果发现①外周血T淋巴细胞亚群的改变T细胞亚群测定结果发现,在两免疫组免疫24h后CD4+/CD8+即开始升高,到第7d时达到一个较高的水平,3个月时开始下降但仍高于同期对照组,第9个月时降至对照组水平,18个月时明显降低;对照组的CD4+/CD8     

阿霉素诱导兔扩张型心肌病模型的建立

目的:探讨阿霉素诱导兔扩张型心肌病模型的可行性。方法:26只兔经耳缘静脉注射阿霉素1m g(/kg.次)×2次/周×8周,用药结束后3周通过彩色超声心动图及病理检查对模型进行评估。结果:存活17只动物,与用药前相比其左室舒张末期内径(LVEDD)及收缩末期内径(LVESD)增大,射血分数(LVEF)及短轴缩短率(LVFS)减低,差别有显著意义(P<0.05),病理检查符合心肌病样改变。结论:通过反复多次注射小剂量阿霉素可成功建立兔扩张性心肌病模型,其病理生理改变与人类临床相符。     

利用心肌功能指数评价窄QRS波的扩张型心肌病患者局部舒缩功能

目的:超声评价窄QRS波的扩张型心肌病患者左室局部心肌的收缩和舒张功能.方法:超声测量21例窄QRS波的扩张型心肌病患者(DCM组)和21例正常人(control组)各二尖瓣瓣环,获得等容收缩期、射血期、等容舒张期、舒张期的持续时间(ICT、ET、IRT、DET),计算评价左室整体和局部心肌综合指数,以及局部收缩期和舒张期心肌功能指数.结果:窄QRS波的扩张型心肌病患者患者左室各壁等容收缩时间(ICT)和等容舒张时间(IRT)明显延长,舒张充盈时间(DFT)缩短,整体和局部心肌综合指数明显增高,局部收缩期(SMPI)和舒张期心肌功能指数(DMPI)也增高.结论:扩张型心肌病时左室整体和局部心肌综合指数明显异常,提示左室局部舒缩功能普遍受损.利用组织多普勒测量整体和局部心肌综合指数可以快速、无创、敏感地评价局部心肌的功能.     

P波离散度与扩张型心肌病的关系

目的：研究P波离散度（PWD）在扩张型心肌病中的表现。方法：研究对象分为两组，研究组为53例扩张型心肌病患者，对照组为53例健康查体者。测量心电图P波最大时限（Pmax）及P波最小时限（Pmin），PWD=Pmax—Pmin。用超声心动图测量左心房内径（LAD）、舒张末期左心室内径（LVEDD）、收缩末期左心室内径（LVESD）及左心室射血分数（LVEF）。结果：扩张性型心肌病患者的Pmax及PWD均明显延长，与对照组相比，差异显著（P〈0．001），而Pmin两组间无显著差异（P〉0．05）。Pmax及PWD与LAD均呈正相关（r=0．533，P〈0．001；r=0．636，P〈0．001），而Pmax及PWD与LVEF均呈负相关（r=-0．672，P〈0．001；r=-0．746，P〈0．001）。结论：在扩张型心肌病患者中PWD明显延长，并与其心功能不全程度明显相关。     

扩张型心肌病患者P波离散度与心房颤动关系的临床研究

目的:研究扩张型心肌病患者P波离散度(Pdisp)与心房颤动的关系。方法:研究对象分为两组,观察组为39例扩张型心肌病患者,对照组为39例健康体检者。测量心电图波最大时限(Pmax)及波最小时限(Pmin),Pdisp=Pmax-Pmin。用超声心动图测量左房内径(LAD)、舒张末期左室内径(LVEDD)、收缩末期左室内径(LVESD)及左室射血分数(LVEF)。结果:扩张型心肌病患者的Pmax及Pdisp均明显延长,与对照组相比,差异显著(P<0.01),而Pmin两组间无显著差异(P>0.05)。Pmax及Pdisp与LAD均呈正相关(r=0.603,P<0.01;r=0.642,P<0.01),而Pmax及Pdisp与LVEF均呈负相关(r=-0.559,P<0.01;r=-0.694,P<0.01)。结论:在扩张型心肌病患者中Pdisp明显延长,并与其心功能不全程度明显相关。     

CRT 对扩张型和缺血性心肌病的左室机械重构疗效观察

目的 观察心脏再同步化起搏治疗（CRT）对扩张型和缺血性心肌病的左室机械重构疗效差别。 方法 入选21 例慢性充血性心力衰竭患者,分为扩张型心肌病组（13 例）和缺血型心肌病组（8 例）。所有 患者均符合CRT 指南的I 类适应证。分别观察CRT 术后6、12 个月左室射血分数、左房内径、左室收缩内 径、左室舒张内径、左室收缩末期容积、左室舒张末期容积及二尖瓣反流面积的变化。结果 ①扩张型心肌病 组CRT 术后6 个月,左室射血分数较术前增加,左室舒张和收缩末内径,左室舒张和收缩末容积,二尖瓣反流 面积较术前减少（P <0.05）,术后12 个月,左室射血分数较术前增加,左室舒张和收缩末内径,左室舒张和收 缩末容积,左房内径较术前减小（P <0.05）;②缺血性心肌病组术后12 个月射血分数较术前增加（P <0.05）; ③扩张型心肌病组CRT 术后6 个月二尖瓣反流面积的变化量大于缺血性心肌病组（P <0.05）,射血分数增加 量大于缺血性心肌病（P <0.05）,术后12 个月扩张型心肌病组左室收缩末内径、左室舒张和收缩末容积的变化 量大于缺血性心肌病组（P <0.05）。结论 CRT 对扩张型心肌病患者的心室逆重构效果优于缺血性心肌病患者。     

Balb/c小鼠CVB3病毒性扩张型心肌病并心力衰竭模型的建立

目的 建立慢性病毒性心肌炎、扩张型心肌病并心力衰竭的实验模型。方法 用CVB3反复感染Balb／c小鼠，分别于感染后第1、3、6、9个月不同时点，采用超声心动图观察小鼠左心室收缩期及舒张末期内径及射血分数。取心肌经HE染色观察其病理形态特征，VG染色观察心肌纤维化，及原位末端标记法观察细胞凋亡。结果B超发现，感染病毒后小鼠左心室收缩末期及舒张末期内径增大，左心室射血分数(EF)下降，与正常小鼠相比P＜O．050反复感染病毒3个月内组织病理学特征与慢性心肌炎类似，而3个月后则呈现出典型的扩张型心肌病理特征。在慢性期主要是病变部位的炎症细胞及心肌细胞凋亡，而扩张型心肌病期出现心肌细胞散在性凋亡。结论 Balb／c小鼠反复感染病毒可能是慢性心肌炎演变为扩张型心肌病并心力衰竭的良好的实验模型；心肌间质纤维与细胞凋亡在心肌炎演变为扩张型心肌病发病过程中起重要的作用。     

低钾对扩张型心肌病跨室壁复极不均一性的影响

目的　研究低钾是否为扩张型心肌病 (DCM )发生室性心律失常的重要促发因素及其电生理机制。方法　将家兔随机分成DCM实验组及正常对照组 ,建立DCM家兔模型并进行离体心脏灌流 ,观察低钾时两组之间 3层心肌APD及跨室壁复极离散度 (TDR)的改变。结果　低K+ 灌流时DCM实验组和正常对照组中层心肌细胞单相动作电位复极 90 %时程 (APD90 )、TDR均长于正常K+ 灌流 (P <0 0 0 1) ,但以DCM实验组延长更为明显 (P <0 0 0 1)。结论　低K+ 延长中层心肌细胞APD ,增加跨室壁复极不均一性 ,可能是DCM易发室性心律失常的重要促发因素。     

实验性轴索型格林巴利综合征兔血清抗空肠弯曲菌脂多糖抗体研究

目的 :探讨轴索型格林巴利综合征 (GBS)兔模型血清中抗空肠弯曲菌脂多糖 (LPS) Ig G抗体的改变。方法 :采用酶联免疫吸附试验 (ELISA)方法检测注射 LPS后发病兔 3只 ,未发病兔 2 3只及对照组兔 1 0只血清中抗 LPS Ig G抗体滴度。结果 :发病兔血清中抗 LPS Ig G滴度最高 ,A值明显高于未发病兔组及对照组 ,P<0 .0 1。未发病兔组血清中抗 LPS Ig G抗体滴度也有升高 ,明显高于对照组 ,P<0 .0 1。结论 :注射 LPS后可使兔体内产生抗 LPS Ig G抗体 ,而且产生抗 LPS Ig G抗体滴度越高者患轴索型 GBS可能性越大。     

Measles immunization. Successes and failures

As a result of a large outbreak of measles, measles hemagglutination inhibition (HI) titers were measured in 465 immunized children. Titers of less than 1:4 were found in 14.6% of children immunized at 12 months of age as compared to 5.2% of those immunized at 13 months of age or later. Measles antibody titers were higher in the mothers of seronegative children who had been immunized at 11 or 12 months of age than in the mothers of seroposotive children. Measles HI titers of 1:4 or more were present in 94% of children immunized at 13 months of age or later between 1962 and 1964. The findings suggest that vaccine failure and not waning antibody accounts for the majority of titers of less than 1:4 in immunized children. Reimmunization programs should be considered for those who were immunized before 13 months of age.